Method for obtaining adhesion between olefin copolymers or terpolymers and natural or synthetic rubbers



May 26, 1970 TORT] ET AL 3,514,357

METHOD FOR OBTAINING ADHESION BETWEEN OLEFIN COPOLYMERS OR TERPOLYMERSAND NATURAL OR SYNTHETIC RUBBERS Filed July 21, 1965 2 Sheets-Sheet l 50I 12- I 'l g 40- i 40 I I 1' l 30 5 9 E I I o 4- v ZI o 20- 2 u 2- 3| 1F: I 10 i 0 1 2 5 4 5 s 7 :8 FIG 0 1 2 3 4 5 6 7 8 FIG.1

I 4- '1 4- r l l FIG. 3 F|G.4

1 INVENTORS LU [GI TORT! TEFANO HRRCELI-O M 60:00 BERTELL! il k. QM

United States Patent 01 Efice 3,514,357 Patented May 26, 1970 Int. Cl.B32b 2 5/04, 27/06, 25/16 U.S. Cl. 156-306 21 Claims ABSTRACT OF THEDISCLOSURE A method of bonding olefin copolymers or terpolymers tonatural or synthetic diene rubbers by covulcanizing the two types ofrubber in direct contact, the diene rubber having a siliceous filler.

The present invention relates to a process for obtaining the adhesion oflinear saturated amorphous copolymers of ethylene with a higheralpha-olefin, or of terpolymers of ethylene with a higher alpha-olefinand a cyclic or acyclic polyene having non-conjugated double bonds, tounsaturated natural or synthetic elastomers; and to the vulcanizedarticles thus obtained.

In practice, it is desirable to combine the excellent dynamiccharacteristics (low elastic hysteresis, high rebound elasticity) ofnatural rubber with the superior resistance to abrasion, ageing andchemical agents of certain new saturated or low-unsaturation syntheticrubbers consisting of amorphous elastomeric interpolymers of ethylenewith propylene and, optionally, a cyclic or acyclic diene containingnon-conjugated double bonds.

This is of particular interest in the manufacture or retreading of tiresof combined structure, in which the carcass is made of natural rubber orof another unsaturated rubber having a low elastic hysteresis and a highelasticity, and the tread consists of an olefin copolymer or terpolymer.

The structure of these new elastomers, which is substantially differentfrom that of diene rubbers, in general renders difiicult the adhesionbetween layers of the two materials, due to their dilferent polarity andto the incompatibility between the different rubbers and theirrespective vulcanization systems.

Diene rubbers, as known, are in general vulcanized with sulfur or asulfur-releasing compound and acoelerators, whereas saturated amorphouscopolymers of ethylene with an alpha-olefin require for theirvulcanization systems based on organic peroxides and on a free-radicalacceptor such as, e.g., sulfur.

It has been proposed to eifect adhesion between layers of natural orsynthetic diene rubber and of elastomeric saturated amorphous copolymersof ethylene with a higher alpha-olefin by inserting between the twolayers an interlayer consisting of a chlorosulphonatedethylenealpha-olefin copolymer, chemically and physically compatiblewith the other two layers and with their respective vulcanizationsystems, and then vulcanizing the three assembled layers.

According to another known method, the adhesion between a diene rubberlayer and a layer of olefin copolymer containing as vulcanizing agentsorganic peroxides and sulfur in amounts higher than 5% by weight on theweight of the copolymer is effected by carrying out the vulcanization attemperatures higher than 170 C.

For practical reasons, in both of the aforementioned procedures,recourse was made to an intermediate layer of copolymer containing thevulcanizing agents in said proportions, in order to avoid increases inthe cost and problems deriving from an increase in the offensive odor ofthe vulcanizates due to the presence of excessive amounts of vulcanizingagents in the whole layer of copolymer.

It has also been proposed to obtain adhesion between a diene rubberlayer and a layer of olefin copolymer or terpolymer by using a dienerubber containing a White mineral filler and an olefin copolymer orterpolymer having a Mooney viscosity higher than 60. Employing thismethod it is possible to use normal vulcanization recipes for bothlayers and, if desired, to dilute the copolymer or terpolymer of Mooneyviscosity above 60 with, for instance, mineral oils, in order to improveits workability.

These methods have various disadvantages, such as, for example, the needof an interlayer and the fact that, while an adhesion effective understatic stresses may be obtained, the resistance to dynamic and thermalstresses is low.

An object of the present invention is to provide a new method forobtaining an effective adhesion, even under heavy load and hightemperature, between layers of diene rubber and layers of elastomericolefin copolymers or terpolymers, which method does not show theaforementioned inconveniences.

A further object of the present invention is to provide new and valuablevulcanized articles having combined structure and consisting of layersof natural or synthetic diene rubber and of layers of the olefincopolymers or terpolymers.

These and other objects of the invention are accomplished bycovulcanizing a layer of diene rubber containing a reinforcing fillerconsisting of a siliceous material and a layer of the elastomericcopolymer or terpolymer, in direct contact with each other, andinitiating vulcanization of the two types of rubbers substantiallysimultaneously, after a time period sufiicient to permit reciprocalsuperficial diffusion of the two layers in direct contact with eachother.

It is found that excellent adhesion of the diene rubber and theelastomeric olefin copolymers and/ or terpolymers is obtained at bothambient temperatures and at -100 C., and without limitation on theMooney viscosity of either rubber or on the type of vulcanization agentsmixed therewith, provided the essential stated conditions are met,namely, that the layers of the two different kinds of rubber arecovulcanized in direct contact with each other; the reinforcing fillermixed with the diene rubber is a siliceous material, and, after the timeperiod for allowing superficial recriprocal dilfusion of the two layers,the vulcanization of the diene rubber starts substantially concurrentlywith vulcanization of the elastomeric copolymer or terpolymer.

When the mix containing the vulcanization agents is introduced into theMooney viscometer at C., the curve of Mooney viscosity shows, at first,a descending segment, then a more or less horizontal segment, andfinally an ascending segment.

The indicator used for ascertaining concurrent initiation of thecross-linking is the time interval between the first minute after theintroduction of the mix containing the vulcanization agents into theviscometer at 150 C. and the moment at which the curve of Mooneyviscosity begins to ascend with a more or less high slope due to thecross-linking.

In the accompanying drawing,

FIGS. 1 to 7 inclusive are curves to which reference is made in thefollowing discussion.

In FIG. 1, the vulcanization starting time (TIV) is represented by theabscissa of point B of the curve, which plots the course of the Mooneyviscosity of the mix at 150 C. (on the ordinate) as a function of time(on the abscissa) by assuming as time zero the first minute after theintroduction of the mix into the viscometer, ie, the moment the rotor ofthe viscometer in the chamber preheated to 150 C. begins to revolve atthe speed of 2 As exemplified below, it has been found that the adhesionincreases essentially linearly with increase in the TIV, the latterbeing the same for both of the layers in direct contact with each other.In practice, good values for the adhesion 5 kg./cm. at 90 C. by thepeeling method) are obtained with TIVZZ minutes.

This invention thus provides a method for obtaining high values ofadhesion between layers of elastomeric materials having differentvulcanization starting times, more particularly between a layer ofnatural or synthetic diene rubber and a layer of a saturated amorphousethylcue/higher alpha-olefin copolymer and/or a low unsaturationterpolymer of ethylene with a higher alpha-olefin and with a cyclic oracyclic non-conjugated diene containing their respectively effectivevulcanizing agents and reinforcing fillers by convulcanization of thetwo layers placed in direct contact with each other at temperaturesbetween 110 C. and 230 C., preferably between 140 C. and 180 C., themethod being characterized by the diene rubber layer containing asiliceous filler and by the convulcanization of the layers in directcontact with each other being carried out with vulcanization startingtimes which are practically the same and higher than 2 minutes, takingas the vulcanization starting time the interval elapsing between thefirst minute after introduction of the mix into the Mooney viscometerkept at 150 C. and the moment at which the viscosity of the mix beginsto increase due to the inception of the cross-linking reaction.

The particular practical importance of the present method resides inthat, for the first time, it is possible, by the use thereof, to obtainthe required adhesion between diene rubbers and elastomeric olefincopolymers or terpolymers, regardless of the characteristics of the twodifferent types of rubber or elastomers and of the type and amount ofvulcanizing agents used, by observing only the two essential andcritical conditions:

(1) using a siliceous filler in the diene rubber mix; and

(2) making the vulcanization starting times of the two different mixescoincide and exceed a minimum value of 2 minutes.

Thus, once the composition of one of the respective mixes to be used hasbeen fixed, it is possible to obtain the enhanced adhesion by simplydetermining the conditions, namely the type and amount of vulcanizingagents mixed therewith, under which the second of the mixes has the samevculcanization starting time as the first mix. As demonstrated in theexamples below, we have found that maximum adhesion values are obtainedwhen the vulcanization starting time is the same for each of the mixesconstituting the layers in direct contact with each other.

In the practical application of this method, for optimum results, it ispreferable to select the composition of one of the vulcanizable mixes,generally the mix based on diene rubber, and to vary the composition ofthe other vulcanizable mix until the vulcanization starting time (TIV)of the two different mixes is equal. In the case of the mixes based onor comprising the elastomeric ethylene/higher alpha-olefin copolymer,for instance, this can be accomplished readily by varying the type ofperoxide used, that is using peroxides of varying decompositioncharacteristics and vulcanizing effect. If a particular type of peroxideis used, its concentration in the mixture comprising the copolymer canbe varied.

According to another embodiment or principle, one can achieve the sameend by varying the vulcanization 4 starting time of the mix comprisingthe copolymer or terpolymer, by suitable selection of the compositionand Mooney viscosity of the copolymer or terpolymer to be adhered to thediene rubber.

In certain instances, however, the vulcanization starting times of bothmixes can be equalized by varying the composition of the vulcanizingsystem of the diene rubher, that is, the amount of sulfur the amount andtype of accelerator, or, finally, by substituting the peroxidicvulcanization system for the one used conventionally in thevulcanization of the diene rubbers.

The process of the present invention can be applied directly to thedifferent layers forming the article to be manufactured or, e.g., when awhite filler is not required in the diene rubber layer, by using a layerof diene rubber containing silica and interposed between the main layersof diene rubber containing, for example with carbon black, and of olefincopolymer or terpolymer.

In the layer of copolymer or terpolymer, which require, as is known, theuse of reinforcing fillers for the obtainment of good mechanicalcharacteristics, these fillers, for the purposes of the invention, canbe carbon black or a white mineral filler selected from those commonlyused in the rubber industry. However, also in these cases, it has beenobserved that higher adhesion values are obtained when the layer ofcopolymer or terpolymer also contains a siliceous mineral filler.

The main diene rubbers with a relatively high degree of unsaturationwhich can be used in accordance with the present invention comprisenatural rubber, polybutadiene, polyisoprene, styrene-butadienecopolymers, etc., which can be vulcanized with systems comprising sulfuror peroxides.

The saturated amorphous olefin copolymers which can be used inaccordance with the invention are preferably copolymers of ethylene withan alpha-olefin, more particularly of ethylene with propylene orbutene-l, having an ethylene content between 20 and 80% by mols,preferably between 40 and and a molecular weight between 60,000 and800,000, preferably between 80,000 and 500,000. In practice productshaving a Mooney viscosity ML(1+4) at 100 C. between 15 and 150 aregenerally used.

The terpolymers which can be used in accordance with the presentinvention are those comprising ethylene, propylene or butene-l and athird monomer consisting of a cyclic or acyclic non-conjugated diene,for example dicyclopentadiene or cyclooctadiene-l,5, and arecharacterized by the presence of 0.051 double bond per 100 carbon atomsand by an ethylene content between 10 and by mols. The molecular weightsare in the range specified above for the saturated copolymers.

As mentioned above, a specific characteristic of the invention is thetype of reinforcing filler which must be present in the diene rubberlayer. In order to obtain effective adhesion, this filler must besiliceous. Anhydrous silica, hydrated silica, aluminum, calcium ormagnesium silicates comprised in kaolin, talc, various clays, bentonite,etc. are suitable. The amount to be used can vary from 5 to 200 parts byweight, preferably from 20 to parts by weight, per 100 parts of dienerubber.

In the layer of elastomeric copolymer or terpolymer, on the contrary,the filler may be carbon black or a mineral filler of the reinforcingtype such as talc, silica, silicates, alumina, kaolin, clay, etc., inthe aforementioned amounts.

The vulcanizing agents to be used in both mixes are not critical for thepurposes of the present invention provided they are such that the samevulcanization starting time (TIV) is obtained for both mixes. Thesystems Well known in the art for the different elastomers may be used,including, in general, sulfur and accelerators for diene rubbers andlow-unsaturation olefin terpolymers, and organic peroxides and sulfur orother free-radical acceptors for the saturated copolymers.

The organic peroxides can be used, also, for the vulcanization of theunsaturated rubbers.

The vulcanization is usually carried out by heating the mixes, kept incontact under pressure, at temperatures between 100 and 230 C.,preferably between 140 C.

The mixes of Type A, free of vulcanizing agents, are subjected tothermal mechanical treatment for 15 minutes at 200 C. in an inner mixer.

In the following Table 1 are reported the types and the amounts ofperoxides used for the various pairs of and 180 C. mixes A and B, andthe values of adhesion as a function The adhesion reported in thefollowing examples was of the vulcanization starting times. determinedaccording to ASTM D-413/ 39 Machine Meth- TABLE 1 Mix of Type A Mix ofType B TIV of Adhesion, Parts by Parts by the two kg./cm. Peroxideweight Peroxide weight rubbers (at 90 C.)

2,2-bis[4,4-bis(tert.butylperoxy)eyclo-hexyl]- propane 6. 52,2-b1s[4,4-bis(tert.butylperoxy)cyclohexylj-propane 2. 4 40" 22,2,5,5-tetra(tert.butylperoxy)hexane 6.62,2,5,5-tetra(tert.butyiperoxy)hexane 2. 4 1'20" 4. 5 Dicumylperoxide6.2 Dicumylperoxide 2.3 200 5. 5 Tet'rachloro di-tert.butylperoxide 6. 5Tetrachloro di-tert.butylperoxide 2. 4 2302,5-dltnethyl-2,5-rli(tert.butylperoxy)-hexane- 5.81,5-dimethy12,5-di(tert.butylperoxy)-hexyn-3 1.5 3'20" 11. 5

od peeling test; the values are given in kg./ cm.

The preparation of the specimen for the determination of the adhesionvalue is carried out as follows: the mixes which have to adhere arelaminated in a calendar into laminae having a thickness of 3 mm.;rectangles of 16 x 8 cm. are then cut and, after treatment of theirsurface with a solvent such as heptane, benzene, etc., are overlapped.

Moulding and vulcanization are carried out in a press.

The specimens are reinforced with a square fabric on the outer surfacein order to facilitate the peeling meas urement.

From the vulcanized laminae 3 specimens having a width of 2 cm. are cutwith a hollow punch.

The following examples are given to illustrate the pres- As is apparentfrom Table l, the adhesion increases progressively by increasing the TIVand reaches satisfactory values, higher than 56 kg./cm. at 90 C., onlywith TIV values higher than a minimum of 2 minutes- EXAMPLE II Mixes onthe basis of natural rubber, having a given formulation of thevulcanization ingredients, are made to adhere with the same number ofmixes on the basis of ethylene-propylene copolymer containing variousamounts of different peroxides.

The mixes have the following composition:

Rubber mix: Parts by wt.

S e ent invention withoutlumting its cop Natural rubber ed Sheet)ML(1+4) EXAMPLE I 100 c 100 Various pairs of mixes on the basis ofethylene-prop y q ica 40 pylene copolymer and of natural rubbercontaining per- Z1110 OXlde 5 oxidic vulcanizing agents of various typesand in suit- 40 'm hy1 n-bis(4-methyl-6-tert. butylphenol) ableproportions, so that the various pairs of mixes have ti 1 a given valueof progressively increasing vulcanization p enylguanidine 0.5 startingtimes, are prepared. ur 0.4

The mixes have the following composition: p a, alpha'-bis (tert.butylperoxy)-diisopropylbenzene 2,1 M1116s of yp A! Parts by Copolymermix:

y -P py copolymer by mols Ethylene-propylene copolymer (55% by mols ofpQPYlene); ML(1+4) 1 75 of propylene) ML(1+4) 100" C.=60 75 Paraffimc011 15= 25 Parafii i il (See Example I) 25 100 Anhydrous silica 40 100Zinc oxide 2 HAF Carbon black 50 Maleic i 4 Zinc oxide 5 G1 1 6Polymerized 2,2,4 trimethyl-1,2-dihydroquino- S lf 0,75 line(antioxidant) 0.5 Different peroxides Variable Fillet-a1 0.5 Mixes oftype B 0 0.5 Natural rubber (smoked sheet) (ML(1+4) VaflOllS pe X esVariable 100 C.=40) 100 Anhydrous silica 40 In the following Table 2 arereported values of ad- Zinc oxide 5 hesion as a function of TIV betweenmixes on the basis 2,2 methylen-bis(4 methyl-6-tert.butyl-pheofcOpolymers, containing various peroxides, at parity n01) (antioxidant)of eifective peroxidic groups, and the mixes on the basisDiphenylguanidine 0.5 of natural rubber with fixed formulation of thevulcaniz- Difierent peroxides Variable ing agents.

TABLE 2 Adhesion, TIV oi Amounts TIV of kgJem. natural vulcanizationPeroxide type bymols copolymers (at 0.) rubber conditions2,2-bis[4,4-bis-(tert.butylperoxy)eyclohexyl] propane 0. 013 1'00 7. 510, C 2,2,5,5-tetra-(tert.butylperoxy)hexane 0. 013 2'15" 11 2'35 15,165 C Dieumyl peroxide. 0. 013 3'50" 7 30',165 c a-bis(tert.butylperoxy)-diisopropylbenzene 0.0087 4'35 5 40, 165 CTetrachloro di-tert.butylperoxide 0. 013 4'35 2 50, 165 C.2,54limethyl-2,5-di-(tert.butylperoxy)hexane 0. 012 6'00 3. 5 60, 165 C.

EXAMPLE III Mixes based on natural rubber, having fixed formulabyplotting the values of adhesion on the ordinates and the values of TIVof the copolymer on the abscissae reaches a maximum in the zone ofcoincidence of the TIV of both mixes.

EXAMPLE 1V Mixes on the basis of natural rubber having fixed formulationare made to adhere to mixes on the basis of ethylene-propylene copolymercontaining variable amounts of various peroxides.

The mixes have the following composition:

Natural rubber mix: Parts by wt. Natural ruber (smoked sheet) ML (1+4)100 tion of the peroxidic agents, are made to adhere to mixes C =4O 100based on ethylene-propylene copolymer containing varl5 Anh drous silica40 lable amounts of peroxide. Zinc Oxide 5 The mixes have the followingcompositions: 2,2 methyl-bis(4-methyl-6-tert.butyl phenol) (antioxidant)1 Rubber m x- Parts by wt. Diphenylguanidine 05 Natural rubber (smokedsheet) ML (1+4) 2O sulfu 4 100 0:40 100 I) Anhydrous silica u 40 11,0-B1s(tert.buty peroxy)-dusopropyl enzene 2.1

Copolymer mix: Zmc Oxlde 5 Eth lenero lene co ol mer (557 b mols of2,2-methylen-bis(4-methyl-6-tert.butyl phenol) y D W p y n a Xpropylene) ML (1+4) 100 C.=6 75 (annoxldant) 1 Paraffinic oil (seeExample I) 25 Diphenylguanidine 0.5 Sulfur aux -B1s-(ert.butylper0xy)dnsopropylbenzene 2.1 Anhydrous Silica 40 Copolymer mix.2 Ethylene-propylene copolymer (55% by mols of i a 9 6 4 propylene) ML(1+4 100 0:60 75 fi ff f 6 Parafiimc 011 (see Example I) 25 Sulfur .075100 Various peroxides Variable Anhydrous silica 4O The mix on the basisof ethylene-propylene copolymer, Zinc oxide 2 free of vulcanizingagents, was subjected to thermal me- Maleic oxide 4 chanical treatmentfor 15 minutes at 200 C. Glycerol 6 The values of adhesion as a functionof the TIV be- Sulfur, g. atoms/mole of peroxide 2 tween the mixes onthe basis of natural rubber and thea,a'-bis(tert.butyl-peroxy)diisopropyli0 mixes on the basis of theethylene-propylene copolymer, benzene Variable containing differentperoxides, at parity of effective Covulcanization: 40'-165 C. peroxidicgroups, are shown in Table 4.

TABLE 4 Adhesion, TIV of Amounts TIV of the kg./cm. naturalvulcanization Peroxide by mols copolymer (at 90 0.) rubber conditions2,2-bis[4,4-bis(tertbutylperoxy)cyelohexyl] propane 0. 018 40" 11. 0 10,165 C. Dieumylperoxide 0, 018 2'00 11.5 0', 165 C. Gd-bis(tert.butylperoxy)-diisopropylbenzene 0. 012 2'20 13.0 2'35 40, 165C. 2,5-dimethyl-2,5-di(tert.butylperoxy)hexane 0.0175 3'20 13. 5 165 C.2,5-dimethyl-2,5-di(tert.buty1peroxy)hexyn-3 0.012 4'00 10. 5 75, 165 C.

The mix based on the copolymer, free of vulcanization EXAMPLE V agents,was subjected to thermal mechanical treatment in an inner mixer for 15minutes at 200 C.

The values of adhesion, as the function of the TIV, between the mixes onthe basis of natural rubber and those on the basis of ethylene-propylenecopolymer containing the peroxide in variable amounts are given in InFIG. 3, in which the dotted line indicates the TIV of the mix on thebasis of natural rubber with constant formulation, it can be observedthat the curve obtained Mixes on the basis of natural rubber havingfixed formulation of the vulcanizing agents are made to adhere to mixeson the basis of ethylene-propylene copolymer containing variable amountsof an organic peroxide.

The mixes have the following composition:

Rubber mix: Parts by wt.

Natural rubber (smoked sheet) NL (1+4) 100 C.=40 100 Anhydrous silica 40Zinc oxide 5 2,2-methylen-bis(4-methyl-6-tert. butyl phenol)(antioxidant) Diphenylguanidine 0.5 Sulfur 2.5N-cyclohexyl-2-benzothiazol-sulfonamide 1.2

Copolymer mix:

Ethylene-propylene copolymer (55% by mols of propylene) ML (1+4) 100C.:60 Parafiinic oil (see Example I) 25 HAF carbon black 50 Pine tar 0.5Zinc oxide 5 Sulfur 0.5 Polymerized 2,2,4-trimethyl-1,2-dihydroquino-Various peroxides Variable line (antioxidant) 0.5 5 Pine tar 0.5 Table 6gives the values of adhesion, as a function of Sulfur, g. atoms/mole ofperoxide 2 the TIV, between the mixes on the basis of natural rubcad-Bis(tert. butyl-peroxy)diisopropylbenzene her with constant composition andthe mixes on the basis Variable of the olefin copolymers containingdifferent peroxides, Co-vulcanization: 40' at 165 C. at parity ofefiective peroxidic groups.

TABLE 6 Adhesion, TIV of Amounts TIV of the kgJem. natural VulcanizationPeroxide type by mols copolymers (at 90 0.) rubber conditions2,2-bis[4,4.-bis(tert.butylperoxy) cyclohexyl] propane 0. 13 1'00 3.010,165 0 2,2,5,5-tetra(tertbutylperoxyfllexane 0. 013 2'00 7.5 4'30 15,165 C Dicumylperoxide 0- 013 3'50" 10. 30' 165 Ca,a-bis(tert.butylperoxy)-diisopropylbenzene- 8 4'40 11. 0 40, 165 CTetrachloro di-tert.butylperoxide 0. 013 4'40" 5 C2,5-dimethyl-2,5-di-(tert,butylperoxy)hexane 012 10 0', 5 O

The values of adhesion as a function of TIV between the mixes on thebasis of natural rubber containing fixed amounts of sulfur andaccelerators and the mixes on the basis of the olefin copolymercontaining variable amounts of an organic peroxide are given in Table 5.

TABLE 5 TIV Adhesion, TIV of of the kgJem. natural copolymer (at 90 C.)rubber Peroxide parts by weight: 3 20 2' 5 3 20 3.5 4'00 8.5 4'00 10.04'20 10.5 414%: 52 7 20 6.5 8'00 2.5

In FIG. 4, in which the values of adhesion between the two elastomersare reported on the ordinates and the TIV of the mix on the basis ofcopolymers are reported on the abscissae and the dotted line indicatesthe TIV of the mix on the basis of natural rubber with constantformulation, it can be observed that the maximum of adhesion is obtainedwhen the TIV of both mixes coincide.

EXAMPLE VI Mixes on the basis of natural rubber having constantformulation of the vulcanizing agents are made to adhere to mixes on thebasis of ethylene-propylene copolymers containing peroxides, withdifferent vulcanization rates. I

The mixes have the following compositions: 5 0 Rubber mix: Parts by wt.Natural rubber (smoked sheet) ML (1+4) 100 C.=40 100 Anhydrous silica 40Zinc oxide 5 6O 2,2-methylen-bis(4-methyl-6-tert. butyl phenol)(antioxidant) Diphenylguanidine 0.5 Sulfur 2.5N-cyclohexyl-2-benzothiazol-sulphonamide 1.5 65 Copolymer mix:

Ethylene-propylene copolymers by mols of propylene); ML (1+4) 100 C.= 75Paraflinic oil (see Example I) 25 100 HAF carbon black 50 Zinc oxide 5Polymerized 2,2,4-trimethyl-1,Z-dihydroquinoline (antioxidant) 0.5

In FIG. 5, as can be noted, the maximum of the curve obtained byreporting the TIV of the copolymer on the abscissae and the adhesion onthe ordinates is obtained when the TIV of the mixes of the copolymer andof natural rubber practically coincide; the dotted line of this figureshows the TIV of the mix on the basis of natural rubber with constantformulation.

EXAMPLE VH Mixes on the basis of natural rubber, containing variableamounts of peroxide as vulcanization agent, are made to adhere to mixeson the basis of ethylene-propylene copolymer with fixed formulation ofperoxides.

The mixes have the following compositions:

Copolymer mix: Parts by wt.

Ethylene-propylene copolymer (55% of mols a,a-Bis(tert. butylperoxy)diisopropylbenzene Variable amounts Covulcanization: 40' at 165 C.

v The mix on the basis of olefin copolymer, before the addition of thevulcanization agents, was subjected to thermal mechanical treatment for15 minutes at 200 C.

The following Table 7 shows the values of adhesion as the function ofthe TIV between the mixes on the basis of ethylene-propylene copolymerwith fixed formulation and the mixes of natural rubber containing, asvulcanizing agent, a peroxide in various proportions.

TABLE 7 TIV of Adhesion, TIV natural kgJcm. of the rubber (at C.)copolymer Peroxide parts by weight:

As can be observed also in FIG. 6 of the drawing, which illustrates thecurve obtained by plotting the adhesion values on the ordinates and theTIV of the mixes of natural rubber with variable formulation on theabscissae and in which the dotted line indicates the T IV of the mix ofethylene-propylene copolymer with constant formulation, a maximum forthe adhesion between olefin copolymers and natural rubber is obtainedwhen the TIV values of the mixes coincide.

EXAMPLE VIII Mixes on the basis of natural rubber having fixedformulation of the vulcanized agents (sulfur+accelerator) are made toadhere to two different mixes on the basis of ethylene propylenecopolymer containing variable amounts of organic peroxides and havingdifferent Mooney viscosities.

The mixes have the following composition:

Parts of weight Pinetar 0 a.a-bis(tert-butyl-peroxy) diisopropylbenzene.Vanabl Sulfur l Grams atmJrnole of peroxide. No E.Covuleanization: 40165C.

In the following Table 8 are reported the values of adhesion as afunction of TIV between mixes on the basis of natural rubber, with fixedformulation of the cross-linking agents, and the mixes on the basis ofolefin copolymer with different Mooney viscosities and containingdifferent amounts of peroxide.

TABLE 8 Mix on the basis of ethylene- Mix on the basis ofethylenepropylezieiegpolymer with ML propylene copolymer with C.=32 ML(1+4) 100 C.=60

Perox- Peroxide, Adhesion, ide, Adhesion, TIV of parts by kgJern. partsby kg./cm. natural weight TIV (at 90 0.) weight TIV (at 90 0.) rubberFrom this table, as well as from FIG. 7 of the drawing, in which the TIVvalues of the two series of mixes on the basis of coplymer with variableformulation and viscosity are plotted on the abscissae and the adhesionvalue between natural rubber and copolymer are reported on theordinates, and in which the vertical dotted line TIV G.N. indicates theTIV values of the mix on the basis of natural rubber with constantformulation, it can be observed that the maximum values of adhesion areobtained when the TIV values of both mixes of copolymers with ML 60 andML 32 practically coincide with that of the mix of natural rubber, whilethe viscosities alone have no influence on the adhesion.

EXAMPLE IX Mixes having constant composition, on the basis ofpolybutadiene and GRS rubber, type 1500, respectively, are made toadhere to mixes of ethylene-propylene copolymer containing variableamounts of peroxidic vulcanizing agents.

The mixes have the following composition:

Homopolymer mix: Parts by wt.

Polybutadiene (molecular weight of about 100,000 ML 1+4 100 0.:24 100Anhydrous silica Stearic acid l 2,6-di-tert. butyl-4-methylphenol(antioxidant) l Aromatic oil (V.G.C. =O.996, d =1.028) 5 a,oz'-B1S(t6lt.butylperoxy) diisopropylbenzene 3.75

GRS copolymer mix:

Butadiene-styrene copolymer, type 1500 ML (1+4) 100 C.= 100 Anhydroussilica y 40 Stearic acid 1.5 Phenylbetanaphthylamine 1.0 Naphthenic oil(V.G.C.=0.885, d =0.948) 3.0 a,a-Bis(tert.butylperoxy)diisopropylbenzene 3.75

Olefin copolymer mix:

Ethylene-propylene copolymer by mols of propylene): ML (1+4) 100 C.=Parafiinic oil (see Example I) 25 Anhydrous silica 40 Zinc oxide 2Maleic acid 4 Sulfur, g. atom/mole of peroxide 2 a,oc'-BiS (tert.butylperoxy) diisopropylbenzene Variable Covulcanization 40' at 0.

TAB LE 9 TIV of the copolymer/polybuta- Ethylene-propyleneEthylene-propylene copolymer] G RS rubber ethylenediene-adhesion, kg./emTIV of adhesion, kg./cm. TIV of propylene p0lybu- GRS copolymer At 25 C.At 90 C. tadiene At 25 C. At 90 0. rubber Peroxide parts by weight:

13 EXAMPLE x A mix on the basis of natural rubber containing thevulcanizing agents in constant formulation is made to adhere to a mix onthe basis of ethylene-propylenecyclooctadiene-1,5 terpolymer containingvarious vulcanization systems.

The mixes have the following composition:

The retreading of the tire with a tread of ethylenepropylene copolymerand its adhesion to the carcass of vulcanized natural rubber wasobtained by carrying out the following operations:

(1) Spreading the rasped carcass with an adhesive consisting of a 20%heptane solution of the mix on the basis of natural rubber type A ofTable 11.

(2) Application onto the carcass of a sheet of type A mix, having athickness of 1 mm.

(3) Treatment with heptane of the surface of the mineral rubber sheetapplied onto the carcass and of a type B sheet on the basis of copolymer(see Table 11).

'Rubber mix: Parts by wt.

Natural rubber (smoked sheet) ML (1+4) 100 C.=40 100 Anhydrous silica 40Zinc oxide 5 2,2-methylene-bis(4-methyl-6-tert. butylphenyl)(antioxidant) -1 15 Diphenylguanidine 0.5 Sulfur 0.4 u,a'-biS(t6I1Z.butylperoxy)dissopropyl-benzene 2.1

opolymer Mix Mix A Mix B EthyleueIpropylene/cyclooctadiene-l,5terpolymer (53% by weight of propylene, 3.96% by weight ofcyclooctadiene):

ML (1+4) 100 C.=40- 100 100 Anhydrous silica 40 40 Maleic acid 4 4 Zincoxide 2 2 Glycerol 6 6 Phenylbetanaphthylamlne 1Tetramethylthiuramdisulfideu 1 Mercaptobenzothiazoie 0. 5 Sulfur 2 0. 4a,a-bis(tert-butylperoxy) diisopropylbenzene 2. 1

NorE.Covu1canization: 40', 165 C.

The mix on the basis of terpolymer, free of vulcanizing agents, wasthermally pretreated in an inner mixer for 15 minutes at 200 C.

The values of adhesion, as a function of the TIV, between the mixes onthe basis of natural rubber and the mixes on the basis of terpoly-merare reported in Table 10.

Some commercial tires were retreaded with a tread of ethylene-propylene(50:50 by mols) having a Mooney viscosity ML (1+4) 100 'C.=60, extendedwith paraffinic oil in the proportions of 75% of copolymer and 25% ofoil.

The composition of the various mixes is reported in Table 11.

TABLE 11 Composition of the mixes A B 0 Natural rubber (smoked sheet) ML(1+4) 100 C.=40 100 Ethyleneropylenc copolymer (55% by mols CaHa) ML(1+4100 C.=60, 75- 100 100 Paraflinic oil (see Example I), 25 Anhydroussilica 40 40 HAF carbon black. 50 Zinc oxide 5 2 5 2,2-me'tl1ylen-bis(4-methyl-6-tert.buty1(phenol) (antioxidant) 0. 5 Diphenylguanidine 0. 5Polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (antioxidant) 0 1 1Glycerol--. 6 Maleic acid Sulfur 0. 5 0. 6 0. 6a,a-bis(tert.butylperoxy) diisopropylbenzene (at Mix B, before additionof the vulcanizing agents, was subjected to a thermal mechanicaltreatment in an inner mixer for 15 minutes at 200 C.

(4) Application onto the sheet of natural rubber of the type B sheet onthe basis of copolymers, having a thickness of 1 mm. onto the naturalrubber sheet.

(5) Application of the tread (mix C, Table 11).

(6) vulcanization of the assembled tires in a suitable mold at thetemperature of 160 C. for 50 minutes.

These tires were tested on a wheel-road at 60 km./h. 'with a load of 600kg. with highly satisfactory results.

In no case was there a separation of the tread from the carcass.

EXAMPLE XII Some tires were manufactured with a carcass of naturalrubber and a tread of ethylene-propylene copolymer (50:50 by mols) witha Mooney viscosity ML (1+4) C.=660, extended with a parafiim'c oil inthe proportion of 7.5% of copolymer and 25 of oil.

The manufiacture of the tires was carried out as follows:

(1) Arrangement on the drum of the manufacturing machine of the plyingswith the mix on the basis of natural rubber having the followingcomposition:

(2) Application of a 1-mm. thick substrate of mix A of natural rubber(see Table 11).

(3) Treatment with heptane of the natural rubber sheet already appliedonto the carcass and of a sheet of mix B on the basis of copolymer (seeTable 11).

(4) Application of the sheet of mix B, l-mm. thick.

(5) Application of the tread of ethylene-propylene copolymer (mix C ofTable 11).

The tires thus assembled were vulcanized in a suitable mold at thetemperature of C. for 50 minutes.

These tires, tested on a wheel-road at 60 km./h. with a load of 600 kg.,did not show any separation of the tread from the carcass.

EXAMPLE XIII Various pairs of mixes on the basis of natural nubber andof ethylene-propylene copolymer, containing siliceous fillers of varioustypes but the same filler in each pair, were prepared. These pairs of ofmixes were covulcanized by using the same cross-linking agents.

Ethylene-propylene copolymer (55% by mols of propylene); ML(1+4) 100C.=60 75 Paraffinic oil (see Example 1) 25 Siliceous filler 1 40 Zincoxide 5 Maleic acid 4 Glycerol 6 Sulfur 1 0.75 ot,u.'-BiS(tert.butylperoxy) diisopropylbenzene 1 4 When Al silicate is used, itis used in an amount of 100 parts per 100 parts of copolymer instead of40 and the sulfur and peroxide amounts are reduced to 0.6 and 3.4 parts,re spectively.

The mixes on the basis of the olefin copolymer are subjected to athermal treatment at 200 C. for 15 minutes before the introduction ofthe vulcanizing agents.

In the following table are reported the TIV values of the two mixes byvarying the type of siliceous filler, and the adhesion values in thezone of coincidence of the TIV values of the two mixes, as a function oftemperature.

rect contact are introduced into a Mooney viscometer maintained at 150C. and the moment in which the viscosity of the mass starts to rise.

2. The process of claim 1 wherein said second layer comprises anamorphous, saturated, elastomeric, vulcanizable copolymer of ethyleneand a higher alphaolefin, the vulcanizing agent of said second layer consisting of an organic peroxide and a free-radical acceptor.

3. The process of claim 1 wherein said second layer comprises anelastomeric, vulcanizable low-unsaturation terpolymer of ethylene, ahigh alpha-olefin, and a nonconjugated diene selected from the groupconsisting of cyclic and acyclic dienes, the vulcanizing agent of saidsecond layer being sulfur.

4. The process of claim 1 wherein sulfur is the vulcanizing agent insaid first layer.

5. The process of claim 1 wherein said first ayer comprises a dienerubber, and said second layer comprises an amorphous, saturated,elastomeric, vulcanizable copolymer of ethylene and a higheralpha-olefin, the com positions of both of said layers comprisingvulcanizing agents consisting of organic peroxides and a free-radicalacceptor.

6. The process of claim 5 wherein said amorphous, saturated,elastomeric, vulcanizable copolymer is a copolymer of ethylene andpropylene.

7. The process of claim 5 wherein said free-radical acceptor is sulfur.

8. The process of claim 6 wherein said free-radical acceptor is sulfur.

9. The process of claim 1 wherein the siliceous filler in said firstlayer is present in an amount of from 5 to 200 parts by weight per 100parts of the diene rubber.

10. The process of claim 9 wherein the siliceous filler It will beobvious that various changes and modifications may be made in practicingthis invention without departing from its spirit. Therefore, we intendto include in the appended claims all such modifications and variationsin details as will be obvious to those skilled in the art from thedescription and working examples given herein.

We claim:

1. In a process for obtaining improved adhesion between a first layer ofa dienic rubber containing a vulcanizing agent and reinforcing fil ertherefor, and a second layer of a material selected from the groupconsisting of amorphous, saturated, elastomeric, vulcanizable copolymersof ethylene and a higher alpha-olefin and elastomeric, vulcanizableterpolymers of ethylene, a higher alpha-olefin and a non-conjugateddiene selecter from the group consisting of cyclic and acyclic dienesand also containing a vulcanizing agent and reinforcing filler therefor,by covulcanization of the two layers disposed in direct contact witheach other, at temperatures between 110 C. and 230 C., the improvementwherein the layer of dienic rubber contains as the only filler asiliceous filler selected from the group consisting of talc, anhydroussilica, hydrated silica, aluminum silicate, calcium silicate, magnesiumsilicate and Bentonite, and the covulcanization is carried out withvulcanization starting times which are essentially the same for thedienic rubher and for the copolymer or terpolymer and that are higherthan a minimum value of 2 minutes, the vulcanization starting timesbeing taken as the time interval elapsing between the first minute afterthe layers in diis present in an amount of from 20 to 100 parts byweight, per 100 parts of the diene rubber.

11. The process of claim 1 wherein the reinforcing filler in said secondlayer is selected from the group consisting of carbon black, talc,silica, silicates, alumina, kaolin and clay.

12. The process of claim 1 wherein the reinforcing filler in both ofsaid first and second layers is the same siliceous material.

13. The process of claim 1 wherein said diene rubber is natural rubber.

14. The process of claim 1 wherein said diene rubber is polybutadiene.

15. The process of claim 1 wherein said diene rubber is polyisoprene.

16. The process of claim 1 wherein said diene rubber is polyisoprene,and the filler in said first layer is Silica.

17. The process of claim 1 wherein said diene rubber is a copolymer ofbutadiene and styrene.

18. The process of claim 1 wherein said unsaturated amorphous copolymerof ethylene and a higher alphaolefin is a copolymer of ethylene andpropylene containing from 20 to mol percent of ethylene and having amolecular weight of from 60,000 to 800,000.

19. The process of claim 1 wherein said unsaturated amorphous copolymerof ethylene and a higher alphaolefin is a copolymer of ethylene andbutene-l containing from 20 to 80 mol percent of ethylene and having amolecular weight of from 60,000 to 800,000.

20. The process of claim 1 wherein said elastomeric low-unsaturatedterpolymer is a terpolymer of ethylene,

propylene, and dicyclopentadiene having an ethylene content of from 20to 80 mol percent and containing from 0.05 to 1.0 double bond per 100carbon atoms.

21. The process of claim 1 wherein said elastomeric low-unsaturatedterpolymer is a terpolymer of ethylene, butene-l, and dicyclopentadienehaving an ethylene content of from 20 to 80 mol percent and containingfrom 0.05 to 1.0 double bond per 100 carbon atoms.

1 8 OTHER REFERENCES Anon: A Technical Report on Nordel HydrocarbonsRubber, du Pont de Nemours and Company, April (1964), page 15 and titlepage relied on.

Sjothun. vulcanization of Elastomers, Feb. 17, 1964, pp. 13, 14, 42-44,57-59, 391 relied on.

HAROLD ANSHER, Primary Examiner 10 W. E. HOAG, Assistant ExaminerCarpenter 152-354 s CL Falcone 161242 Tavenor et a1 161240 152330;156128; 161--242 Willis et a1. 1s2-3s7 15 mg? UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent 2514 Dated May 264 1970Invencor(s) Luigi Torti Stefano Marcello, and Guido Bertelli It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

EJ lumn 3 line 55 vculcanization" should read vulcanization Column 4,line 8, "sulfur" should read sulfur, lines 17 and 18, "for example withcarbon black," should read for example,

carbon black Column 8, line 13, "ruber" should read rubber line 24, "6"should read 60 Column 10, line 42, "Maleic acid 2" should read Maleicacid 4 Column 11, line 28, "polymer Mixz" should read Copolymer Mix:

line 29,"CopEthylene-propylene" should read Ethylenepropylene-;

line 34, "Pinetar" should read Pine tar line 35, "Variabe2" should readVariable line 36, "'1" should read '2 Column 13, line 55,"ethylene-propylene (50:50 by mols)" should read ethylene-propylene copolymer (50:50 by mols) Column 14,

line 11, "mineral" should read natural line 31 "l00C=660,"

should read l00C=60, line 74, "pairs of of" should read pairs of Column15, line 7 "2,2" should read 2,2'-

Table 13, column marked "90C", "11.00" should read 11.0

' 3.; 1-31.14; ..'ALED J I I. JZR- mi L -Jr. onar or Patents

